Multi-zone HVAC systems (hereinafter ‘HVAC zoned systems’) include one or more components to condition air that enters the system and drive the conditioned air through supply ducts to multiple zones within a building. Each supply duct includes zone dampers that may be adjusted to control a flow of the conditioned air into each zone to achieve a desired temperature and airflow within the zone. When a zone reaches a desired conditioned state, typically, the zone dampers associated with the zone are closed. Since a fixed amount of air is delivered by the air handler of the HVAC system under most operational conditions, when the zone dampers of one zone are closed, additional air is driven through the remaining zones that have open zone dampers which causes static pressure to build up in the remaining zones and affect a balance of airflow and pressure across the HVAC system. The increased amount of air that is driven through any one zone may cause the zone to be over-conditioned and increase a noise level in the zone to undesirable levels. The term ‘static pressure’ as used herein refers to an external static pressure of the HVAC system.
One conventional solution to relieve the static pressure and reduce the airflow noise includes providing a bypass system which includes a bypass damper that allows the excess or additional air to be returned to the return duct and back to the temperature changing elements (heating or cooling coils) of the HVAC system via a bypass duct. However, conventional bypass dampers that are used in the bypass system do not provide any means for precisely controlling the amount of conditioned air that is returned to the return duct and the temperature changing elements of the HVAC system. The inability of the conventional bypass dampers to provide a precise control of the amount of conditioned air that is returned to the return duct may negatively affect the efficiency of the HVAC system and cause additional problems. For example, in a cooling cycle, cold air that is returned to the return duct via the bypass damper of the bypass system may reduce the temperature of the air that reaches the evaporator coil, thereby making the evaporator coil colder and reducing its efficiency. Further in said example, since the conventional bypass dampers do not provide precise control of the conditioned air that is returned to the return duct, sometimes a large amount of cold air may be returned to the return duct which may reduce to the temperature of the air that reaches the evaporator coil to an extent that it could freeze the evaporator coil.
One conventional bypass damper is a mechanical bypass damper that utilizes a weighted arm with a spring and typically includes two damper positions, i.e., a fully open position and a fully closed position. Other conventional bypass dampers, such as modulating bypass dampers that can be incrementally closed to provide control over the amount of conditioned air that is returned to the return duct do exist. However, a flow of conditioned air with a change in damper positions of said modulating bypass dampers exhibit a nonlinear behavior, thereby affecting an ability to accurately determine the amount of air that flows through the bypass damper at each damper position of the bypass damper.
Other solutions to relieve the static pressure and reduce the airflow noise without using bypass systems do exist. One such solution includes smart HVAC zoned systems, such as a multi-stage or modulating HVAC system that does not include a bypass. Instead, the smart HVAC systems use alternate techniques to relieve the static pressure and reduce the airflow noise in the zones where additional air is delivered. Such alternate techniques may include reducing the airflow using a variable speed blower, reducing equipment capacity, dumping into set back zones, etc. However, once the attempts to reduce the airflow noise using the alternate techniques have been exhausted and the airflow noise is still above an undesirable level, then, the smart HVAC system shuts down which in turn may leave one or more zones under-conditioned. For systems that are prone to noise issues, e.g., systems with many zones, or small ductwork, etc., one or more zones may remain under-conditioned regularly.
Therefore, improvements to HVAC systems with zones are described herein. It is noted that this background information is provided to reveal information believed by the applicant to be of possible relevance to the present disclosure. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present disclosure.